Asymmetric cyclic loading behavior of micro-alloyed 2.25 Cr-Mo steel at room temperature

Ratcheting fatigue tests were carried out on the micro-alloyed 2.25Cr-Mo steel with variable mean stress (sigma(m)), stress amplitude (sigma(a)) and stress rate (sigma(s)) at room temperature. Increase in the sigma(m) and sigma(a) resulted in higher plastic strain accumulation and caused a reduction in fatigue life; however, rise in the.s enhanced the fatigue life. Hysteresis loop analysis showed variation in plastic strain range under the different test variables. Transmission electron microscopy (TEM) was carried out to understand the lower plastic strain accumulation resulting from the high sigma. It was observed that at high sigma there was formation of stacking-faults/micro-twins in the M23C6 carbides, due to which there was strain partitioning between the matrix and the carbide particles, consequently, the effective strain in the matrix was reduced. Using mathematical modeling, experimental fatigue life was predicted by the trial and error method. The predicted fatigue life was found within the 1.55X scatter band and there was a reasonable estimation of ratcheting fatigue life.

Automated summary

Ratcheting fatigue tests revealed that increasing mean stress and stress amplitude reduced fatigue life, while increasing stress rate enhanced fatigue life. Experimental results showed varying plastic strain ranges under different test variables.